Building a bubble sort
The classic bubble sort is an exercise often assigned to university students. Nonetheless, it's important to master this algorithm as there are many occasions where built-in PHP sorting functions do not apply. An example would be sorting a multi-dimensional array where the sort key is not the first column.
The way the bubble sort works is to recursively iterate through the list and swap the current value with the next value. If you want items to be in ascending order, the swap occurs if the next item is less than the current item. For descending order, the swap occurs if the reverse is true. The sort is concluded when no more swaps occur.
In the following diagram, after the first pass, Grape and Banana are swapped, as are Orange and Cherry. After the 2nd pass, Grape and Cherry are swapped. No more swaps occur on the last pass, and the bubble sort ends:
How to do it...
We do not want to actually move the values around in the array; that would be horribly expensive in terms...
